In the aerospace field it is ordinary for combustion turbine engines employed for aircraft propulsion to be installed on the aircraft within aerodynamic nacelle structure. Consequently, access to the engine within the nacelle is restricted, and maintenance operations which easily could be performed on the engine apart from the aircraft are rendered difficult and time consuming because of limited access. One of these maintenance operations is the removal, inspection, and reinstallation of fuel nozzles. Because fuel nozzles of a combustion turbine engine extend into the combustion chamber and are exposed to considerable heat as well as the possibility of carbon deposit formation, their inspection on a regular schedule is one of the more frequent maintenance procedures. Also, because a defective or carbon fouled fuel nozzle can result in uneven fuel atomization and resulting combustion hot spots which could damage an engine, this maintenance procedure is vital to insuring proper service life for an engine.
Traditionally, because conventional fuel nozzles are secured to the outer casing of a turbine engine by bolts threading into the engine casing, the bolt heads have been cross drilled and aircraft safety wire installed to insure that the nozzles do not loosen between inspections. Conventional aircraft safety wiring practices are long established, low in material cost, and result in a very reliable mechanical installation which resists loosening of the nozzle bolts consequent to vibration from engine operation. However, safety wiring of bolts in the confines of an aircraft engine nacelle is very time consuming, high in labor cost, and is difficult because of the contortions required of the aircraft mechanic.
Thus, it has been recognized in the field that a substitute for safety wiring of inaccessible fasteners on aircraft is highly desirable. The requirements for such a safety wire substitute are simplicity, low cost, ease of use, and near-absolute reliability. Conventional fastener retention or locking expedients known to the applicant and which are possibly relevant to the present invention are set forth by the following United States patents:
______________________________________ U.S. Pat. No. Inventor Name Issue Date ______________________________________ 382,789 L. J. Benton May 15, 1888 2,385,777 J. F. Ebert Oct. 2, 1945 2,421,201 R. L. Hallock May 27, 1947 2,424,521 A. Utsch July 22, 1947 2,758,628 C. M. Rice Aug. 14, 1956 2,620,008 L. L. Mallard Dec. 2, 1952 2,783,674 P. D. Becker March 5, 1957 3,467,417 R. Ollis, Jr. et al Sept. 16, 1969 ______________________________________
Unfortunately, not one of these known fastener locking techniques is fully satisfactory. Some of these fastener locking schemes are too complex in their structure, or require specially configured fasteners, others would be difficult to use in a confined location, or cannot assure the near-absolute level of reliability required for aircraft use. Also, several of these conventional fastener locking expedients are too expensive to be viewed favorably as a substitute for the traditional low-cost safety wire method of locking fasteners.